1. Field of the Invention
The present invention relates to a lesion extracting device and a lesion extracting method, which can determine a lesion part based on a fluorescence image produced with irradiation of an excitation light.
2. Description of Related Art
Recently, development has been progressed on a technique for diagnosing a cancer or other affected state of body tissues by using a medicament which is accumulated in an affected part, such as a cancer, and which emits fluorescence with irradiation of an excitation light.
In particular, there is known a technique of irradiating an excitation light to a biomedical body from, e.g., a fluorescence endoscope after injection of the medicament into the body, detecting fluorescence generated from the medicament, which has been accumulated in the affected part, in the form of a two-dimensional image by using, e.g., the fluorescence endoscope, and diagnosing the affected part based on the detected fluorescence image (see, for example, Japanese Unexamined Patent Application, Publication No. Hei 7-222712 and No. 2004-477).
The above-described diagnosis using fluorescence has the problem as follows. When a normal part and a lesion part or a benign tumor and a malignant tumor are present in the same field of view for observation, it is often difficult to discriminate the normal part and the lesion part or the benign tumor and the malignant tumor from each other.
More specifically, in the diagnosis using fluorescence, comparing the normal part and the lesion part, the intensity of fluorescence generated from the lesion part is stronger than that emitted from the normal part. Comparing the benign tumor and the malignant tumor, the intensity of fluorescence generated from the malignant part is stronger than that generated from the benign part. In general, the intensity of the fluorescence generated from the lesion part is proportional to the intensity of the excitation light irradiated to the lesion part. Accordingly, when the intensity of the excitation light irradiated to the normal part (benign tumor) is stronger than the intensity of the excitation light irradiated to the lesion part (malignant tumor), the intensity of the fluorescence generated from the normal part or the like is stronger than that generated from the lesion part or the like. The above-mentioned problem may occur, for example, when the distance from the tip of an insertion probe of the fluorescence endoscope differs between the normal part and the lesion part or between the benign tumor and the malignant tumor.
Another problem is that, even when the distances to the normal part and the lesion part are substantially the same, a difficulty may occur in discriminating the normal part and the lesion part or the benign tumor and the malignant tumor in some cases.
More specifically, when the lesion part or the like is positioned inside the body, the intensity of the fluorescence generated from the lesion part or the like is attenuated while passing through the body. In such a case, when simultaneously observing the fluorescence generated from the lesion part or the like and the fluorescence generated from the normal part or the like which is positioned at the body surface, the difference between the intensity of the fluorescence generated from the normal part or the like and the intensity of the fluorescence generated from the lesion part or the like is reduced. In other words, the intensity of the fluorescence generated from the lesion part or the like is reduced. This may cause a difficulty in discriminating the normal part and the lesion part or the benign tumor and the malignant tumor from each other.
As one of other methods for quantitatively discriminating the normal part the lesion part, there is known a method comprising the steps of irradiating an excitation light having a plurality of wavelengths to a part to be observed, and analyzing a fluorescence spectrum emitted from the observed part. However, because the fluorescence spectrum contains a very large amount of information, the above method has the problem that it is difficult to extract predetermined information, which is used for determining the normal part and the lesion part, from the fluorescence spectrum and to perform a quantitative analysis.